The major thrust of research in our group during the next five years will be directed toward gaining a better understanding of molecular mechanisms for regulation of cell differentiation and development. For this work, we will continue to study hepatocytes -using chick embryo liver both in vivo and in vitro because of its rapid growth rate and high gluconeogenic capacity. Currently our research efforts are centered around the purification and characterization of three compounds involved in these differentiation processes: (a) a low molecular weight factor from chicken liver which stimulates the aggregation of chick embryo liver cells (HAP), (b) another, low molecular weight factor, also from chicken liver, which inhibits the enhancement of aggregation by HAP, and (c) a specific glycoprotein excreted by chick embryo liver cells grown in monolayer, which binds tightly to isolated suspensions of liver cells. Studies on the physiological role of these factors in development and maintenance of differentiated function will be extended as we learn more about their molecular functions.